As a known fact in the relevant background art, the top surface course on the base is realized on the road's foundation by applying asphalt concrete mixed with bitumen according to various methods (hot mix, warm mix, etc.) in the form layers with differing characteristics one layer on the other. Each asphalt concrete layer has differing performances and is obtained by mixing aggregates provided by breaking off natural stones with bitumen in certain proportion according to standard design methods. The asphalt layers and particularly the surface layer (i.e. the wear course) making up the road's top surface course have certain lifespan. Any such layers with expired lifespan or which must be renewed as it becomes nonfunctional due to deformation under various influences must be ripped from the place it was already paved. Any such asphalt to be recycled and therefore subjected to this operation is named as RAP, i.e. Reclaimed Asphalt Pavement, while the asphalt recycled as a result of various methods to be detailed hereinafter is designated as Recycled Asphalt Concrete, i.e. RAC.
The procurement of aggregate from mines which are rarely found in many regions of the world but particularly in the Europe continent, the transport of such aggregate to production facilities and their processing brings about high costs. The other raw material, i.e. the bitumen, used in producing the asphalt concrete is obtained from petroleum. The recycling of removed reclaimed asphalt pavement (to be referred to hereinafter as RAP, or RAP material) removed from its original place instead of discarding it brings economical and environmental advantages with respect to reducing the raw material supply costs for producing asphalt concrete, the efficient use of natural sources (e.g. aggregate and bitumen) consumed in relevant processes, and eliminating the cost of management of any such removed reclaimed asphalt pavements as a constructional waste material.
Depending on available conditions, it is possible to pave back the RAP material to its original place by implementing a process bringing it back to a reusable condition at the site of removal (i.e. in situ recycling). In some other circumstances, it is dismantled and transported away from the original place so as to be admixed into new hot asphalt concrete mixture prepared at the asphalt plant where fresh asphalt concrete is produced. Before being admixed, it can be subjected to breaking-off and/or sieving operation(s) and be classified with respect to aggregate size so that its admixture will not deteriorate the desired specifications (the mixture gradation, bitumen rate, etc.) of the fresh hot asphalt concrete mixture.
RAP material, which is already classified according to the aggregate size may be added in the cold form to the new hot asphalt concrete mixture (i.e. cold recycling), in this case however, the addition proportion may become restricted. Since any such ripped asphalt added in the cold form will drop down the temperature of the new mix, the proportion in which the ripped asphalt is added must be kept at lower levels.
The most efficient way of producing a new hot asphalt concrete mix with the highest RAP proportion possible is to heat RAP before adding it into the mix. If the RAP material is to be heated and fed into the asphalt plant in an amount (tones/hour) required for the new mixture, it is possible to produce the new mix from 100% of RAP material.
Because of both economical and environmental factors referred to hereinabove, the intention for producing a new hot mix asphalt by means of a maximum RAP material proportion becomes very understandable.
Although the systems enabling the addition of RAP material in a hot form into the new mix allows to a relatively higher mixture proportion for RAP, the maximization of this proportion is difficult due to some drawbacks of current technologies. Put differently in a more detailed manner, RAP material becomes sticky as it is heated before fed into the mix because of the bitumen contained therein, and becomes adhered to the walls of means (drum, elevator, etc.) wherein it is heated and transferred to the new mix. Since it becomes adhered and coated to the inner walls of such heating and transfer means, the internal volume of such means becomes diminished following each use. Thus, even if the RAP material accumulated in such means can partially be cleaned, it nevertheless causes a substantial reduction in the system's efficiency and capacity; in other words, the amount of RAP material supplied to the new mix becomes gradually reduced so that the system's capacity becomes lower and lower or even entirely blocked.
Despite the fact that mixing RAP material into the new mix provides some advantages, the difficulties experienced in maximizing the admix proportion of RAP material in producing new asphalt require an improvement be made in the relevant technical field.